Extreme Ultraviolet (EUV, 13.5 nm) imaging technology continues to be the primary option for the 22 nm microelectronics node. However, EUV resist performance remains one of the largest barriers to EUV technology implementation, because it is difficult to simultaneously meet performance targets for resolution, line width roughness (LWR) and sensitivity. For example, low concentrations of acid during imaging will yield rough lines (high LWR), but good sensitivity; high concentrations of acid will give smoother lines, but poor sensitivity. To break through to a new level of performance, new materials must be developed that will make improvements toward one performance target without compromising the performance of the other two.
Acid-cleavable polymers are known in the art. In an early approach to a deep ultraviolet (DUV or 248 nm) photoresist or a 193 nm photoresist, the polymer has an ester with a side-chain blocking group (e.g. t-butyl) that can be removed with catalytic acid, and a photoacid generator (PAG) is randomly dissolved within the polymer film, so that exposure to actinic radiation yields a developer-soluble carboxylic acid. Typical first-generation ionic PAGs are sulfonium and iodonium salts. These resists are relatively inexpensive and simple to prepare using standard formulation methods. The resists have high sensitivity because acids are free to diffuse through the film, catalyzing acidolysis reactions (removal of ester blocking group) with large turnover numbers. In a second approach, for which the monomers of the present invention are also useful, the photogenerated acid is integrated into the polymer chain. This approach is described in PCT application PCT/US09/34707 filed Feb. 20, 2009, which is incorporated herein by reference. PCT/US09/34707 relates to a resist system based on a polymer with PAG and ester functionality located within the main polymer chain. When the PAG breaks apart photochemically or the ester-linkages break apart by acidolysis, the molecular weight of the polymer decreases, allowing for higher acid diffusion during bake and faster resist dissolution during development. The polymer of PCT/US09/34707 is referred to as a chain scission polyester PAG-polymer (CSP3). With CSP3 the photochemical reaction breaks the polymer chain and produces a polymer-bound acid at a chain end. Then, the photogenerated acid catalyzes the transformation of the ester to the developer-soluble carboxylic acid by once again breaking the polymer chain. For either approach—PAG dispersed in resin or PAG incorporated in polymer—the monomers of the present invention provide additional acid-cleavage sites. The resulting areas of the resist exposed to light and subjected to acidolysis reactions have much lower molecular weight resulting from the chain scission reactions. This provides lower Tg, higher acid diffusion rates, and faster dissolution rates.